Add webfinger redirection for sub-path (ActivityPub actor visibility)

[lapineige]

Fixes https://github.com/YunoHost-Apps/wordpress_ynh/issues/61.

For subpaths, ActivityPub actor is not discoverable, the json file at WebFinger endpoint is not reachable.

PR Status

• [x] Code finished and ready to be reviewed/tested
• [x] The fix/enhancement were manually tested (if applicable)

Automatic tests

Automatic tests can be triggered on https://ci-apps-dev.yunohost.org/ after creating the PR, by commenting "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!". (N.B. : for this to work you need to be a member of the Yunohost-Apps organization)

[ericgaspar]

!testme

[yunohost-bot]

:v:

[lapineige]

Looks fine except change URL…